(a) Field of the Invention
The present invention relates to a receiving apparatus and method for an RFID reader, and more particularly, to an RFID which can reduce the tag recognition rate decrease caused by multipath fading.
(b) Description of the Related Art
Generally, RFID technology provides services such as positioning, remote processing, and managing of objects, information exchange between objects, etc., by attaching tags to each object, wirelessly recognizing unique identifiers (IDs) of the objects, and collecting, storing, processing, and tracking the corresponding information on the objects. The RFID technology is forecasted to form a new market by replacing the existing barcode and being applied to various fields such as material management, distribution, security, and so on.
A 900 MHz UHF RFID system is a passive type, and a data transmission scheme thereof uses backscatter modulation. The backscatter modulation is a method that transmits information on tags by changing the magnitude of scattered electromagnetic waves when the tags scatter continuous waves (CWs) sent from the reader and returns them to the reader.
According to the communication protocol of the passive RFID system, when the reader transmitter receives a baseband signal from a digital processor, for example, a modem, it alternately transmits a modulation signal and a continuous wave signal. When the reader transmitter transmits the modulation signal, the tag only receives the modulation signal but does not transmit a response signal, and therefore the reader receiver receives no signal. On the other hand, when the reader transmitter transmits a continuous wave, the tag transmits a response signal, and therefore the reader receiver receives and processes the response signal.
The tag absorbs a part of the continuous wave signal from the reader and reflects the rest of it. The reflected signal is a response signal from the tag. The tag information can be carried by changing the reflectivity.
The reader can receive the response signal while transmitting the continuous wave signal. Therefore, the reader uses the same frequency for transmission and reception.
Regarding data transmission between the tag and the reader, a continuous wave signal transmitted from the reader via a wireless communication channel returns as a backscatter modulated signal having the same frequency through tag impedance mismatch. At this time, the magnitude and phase of the returning backscatter modulation signal are severely distorted due to multipath fading in the surrounding environment or due to inter-tag interference caused by a high concentration of tags. This makes it difficult for the reader receiver to restore a response signal from a tag, thereby causing a decrease in tag recognition rate.